Internal combustion engines, in particular diesel engines and spark ignition engines, are increasingly provided with compressors for the air which is fed to the engine. A considerable increase in power can be obtained by compressing the charge air which is fed to the engine. Conversely, a predefined power can be achieved by a supercharged engine with a relatively small cubic capacity, as a result of which a relatively small and relatively lightweight design can be achieved and the vehicle can be driven in a way which is more economical in terms of the consumption of fuel.
Such compressors can be embodied, for example, as exhaust gas turbochargers or else as engine-operated compressors. Exhaust gas turbochargers are driven by the stream of exhaust gas of the internal combustion engine. The turbocharger has for this purpose a turbine which is arranged in the stream of exhaust gas and which drives a compressor which compresses the charge air of the engine. Such a compressor can, however, also be driven by the internal combustion engine via a belt drive or directly by means of the crankshaft.
Since an exhaust gas turbocharger is driven by a turbine which is arranged in the stream of exhaust gas, the compression effect and therefore the increase in power of the internal combustion engine are dependent on the stream of exhaust gas; a perceptible increase in the torque therefore occurs only at relatively high rotational speeds of the internal combustion engine. A compressor which is driven by the internal combustion engine can also make available an increased charge pressure even at a relatively low rotational speed; however, such a compressor requires a considerable portion of the power which is made available by the internal combustion engine.
For these reasons, combinations of an exhaust gas turbocharger with a compressor (often also referred to as a “supercharger”), driven by the internal combustion engine, are also used, wherein both compressors operate in parallel with one another or in series. In order to avoid the consumption of power by the compressor when the compressor is not required, it is possible, for example, to provide a clutch which decouples the compressor in the idling mode of the internal combustion engine.
When a motor vehicle starts, the situation generally occurs in which, by activating the accelerator pedal, the driver requests a large torque in order to accelerate the motor vehicle, but the compressor or compressors for supercharging the engine are, owing to the idling state of the engine, not in an operating state in which the engine can be supplied with an effective charging pressure. For this purpose it is desired, for example, to reach a sufficient rotational speed for the exhaust gas turbocharger and to close the clutch of the compressor; only when the respective compressor has itself reached a sufficient rotational speed is it possible for the internal combustion engine to be provided with a charging pressure which gives rise to the desired increase in the torque or power. In the case of an engine which is of relatively small design for reasons of economy, and in order to achieve the desired power, is provided with one or more charge air compressors, only a relatively low power is therefore available at the beginning of a starting process.
This applies, in particular, when unfavorable ambient conditions apply in which the internal combustion engine only outputs a reduced torque or a reduced power owing to the thermodynamic conditions, that is to say, for example, in the case of the reduced air pressure at high altitude or of high external temperatures. This is particularly problematic when an increased torque is already desired for starting, for example if the motor vehicle is located on an uphill slope and has an increased mass, for example owing to a trailer. In such cases, the torque available for starting is frequently insufficient.
The object of the present description is to provide a method and a device for controlling the starting of a motor vehicle which is driven by a supercharged internal combustion engine, with which method and device the abovementioned disadvantages do not occur.
This object is achieved by means of a method and a device such as are disclosed in the claims. In the case of a motor vehicle which is driven by an internal combustion engine which is supercharged by at least one compressor, the beginning of a starting process is detected. This can already occur at a very early time, in particular before the driver requests an increased torque, for example by depressing the accelerator pedal by a corresponding amount.
According to the description, at least one operating parameter of the motor vehicle and/or at least one environmental parameter are/is sensed. Corresponding sensors may be provided for this purpose, the signals of which sensors are sensed and evaluated. The at least one compressor is activated in a predictive fashion if the at least one operating parameter and/or environmental parameter is outside a predetermined range (e.g., a desired range) of values of the parameter. In order to activate the compressor, it is possible, for example, to close a clutch, by means of which the compressor is driven by the engine, or else to activate an electric drive of the compressor so that the compressor is driven and builds up the charging pressure.
By activating the compressor in response to the environmental parameter it may be possible to provide a desired engine output torque at the time of starting and as the driver increases the engine torque demand. For example, pressurized air may be provided to the engine air intake during engine cranking and as engine speed accelerates to achieve idle speed. Further, when the engine can provide the desired level of torque at the existing environmental conditions without aid of the compressor, the compressor may not be activated during cranking and engine run-up to idle speed so that fuel consumption may be reduced.
The present description may provide several advantages. Specifically, the approach may provide a desired amount of engine torque during starting over a wide range of environmental conditions. Further, the approach may conserve fuel by not activating a compressor during engine starting when the engine does not need the compressor to provide the desired engine output torque.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.